The present invention relates to cleaning apparatuses for removing oily waste from articles to be cleaned, and is directed more particularly to cleaning apparatuses that make use of water-based cleaning liquids. Cleaning apparatuses of this type are also commonly referred to as parts washers or cleaners.
The machining and use of articles such as machine parts, automobile parts, etc. often leaves these articles contaminated by a coating or film of oily waste. In the case of machine parts this coating often includes particles or chips of metal produced during machining. In the case of auto parts this coating often holds particles of dirt dust and the like that become trapped therein during driving. In order to remove such particles, and prevent the trapping of additional particles, it is necessary to remove substantially all of the oily waste that serves as the retaining matrix thereof.
Prior to the present invention many different approaches have been used in an attempt to safely and efficiently solve this problem. One class of these approaches has been the use of non-polar organic cleaning liquids such as kerosene, gasoline, hexane, etc. which act as solvents for oily waste. While these materials are highly effective, their flammability, toxicity and disposal problem makes their use undesirable. In addition, the ability of such cleaning liquids to form true solutions with oily substances causes the accumulation of such substances therein until the cleaning liquids becomes unusable and must be disposed of as hazardous waste.
Yet another class of these approaches has been the use of plain water to suspend or entrain oily waste under conditions of high agitation, and to thereafter separate out the oily waste under conditions of low agitation. The separation phase of this approach is accomplished with a separating apparatus which takes advantage of the natural immiscibility of oil and water. Examples of separating apparatuses suitable for use with this approach are described in U.S. Pat. Nos. 4,717,475 (Brandt et al) and 3,957,656 (Castelli).
Another class of these approaches has been the use of water based cleaning liquids, such as those which use soaps or detergents, that emulsify the oily waste and take the resulting emulsion into suspension. While cleaning liquids of this type are not a fire hazard, they too accumulate oily waste until they become unusable and must be disposed of as hazardous waste.
Still another class of these approaches has been the use of water based, non-emulsifying cleaning liquids such as those which include various mixtures of surfactants, semi-polar organic solvents, wetting agents, etc. that have the ability to suspend or take up oily waste under a first range of conditions and to release that waste under a second range of conditions. The use of such cleaning liquids not only has many of the advantages that are associated with approaches that use plain water, but also has none of the disadvantages that are associated with the use of approaches that use mixtures of water and detergents. One example of a cleaning apparatus that uses non-emulsifying cleaning liquids is described in U.S. Pat. Nos. 5,232,299 (Hiss) and 5,303,725 (Hilgren). Another example of a cleaning apparatus that may use a cleaning liquid of the last-mentioned type is described in U.S. Pat. No. 4,817,649 (Schmalz et al).
Cleaning apparatuses that use emulsifying or non-emulsifying cleaning liquids are ordinarily of one of two broad types. A first of these types, hereinafter referred to as the immersion type, includes a dip tank within which the articles to be cleaned are placed within a tank containing a body of cleaning liquid having a depth sufficient to cover those articles. The second of these types, which may be referred to as the non-immersion includes a shallow basin or tray within which the articles to be cleaned are placed and exposed to the flow or spray of a cleaning liquid with which they may be scrubbed and rinsed. Intermediate types of cleaning apparatuses, e.g., apparatuses in which the articles to be cleaned are partially immersed or are both immersed and brushed, are also known. All of these types of apparatuses may include a settling tank within which part of the entrained oil may be separated from the cleaning liquid and a pump for recirculating such partially cleaned liquid to the cleaning area.
Prior to the present invention both of the above-mentioned types of washers had disadvantages which limited their usefulness. Non-immersion type washers, for example, tend to spill or splash cleaning liquid onto their surroundings and into the air. Immersion type washers, on the other hand, tend to develop a surface layer in which oily waste becomes concentrated and which can re-contaminate a cleaned article when the latter is lifted from the tank. While various types of overflow structures have been used to skim off this oil-rich surface layer and return it to the tank after most of the oil has been removed therefrom, the operation of such overflow structures is subject to disruption by the sudden changes in surface level that accompany the addition of articles into and removal of articles from the tank.